Precoding reference signals for uplink transmission with downlink interference information

ABSTRACT

Certain aspects of the present disclosure relate to methods and apparatus relating to precoding reference signals for uplink transmissions with downlink interference information. In certain aspects, a method, performed by a user equipment (UE) comprises receiving, from a base station, one or more signals for use in estimating channel quality for a downlink between the base station and the UE. The method also includes determining a first frequency resource and a second frequency resource from a frequency band allocated for transmitting a reference signal (RS). The method further includes computing a first downlink channel quality estimate for the first frequency resource using the one or more signals, transmitting a first RS precoded using the first downlink channel quality estimate, computing a second downlink channel quality estimate for the second frequency resource using the one or more signals and transmitting a second RS precoded using the second downlink channel quality estimate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is continuation of U.S. application Ser. No.16/059,603, entitled “PRECODING REFERENCE SIGNALS FOR UPLINKTRANSMISSION WITH DOWNLINK INTERFERENCE INFORMATION,” which was filedAug. 9, 2018, and which claims the benefit of U.S. ProvisionalApplication Ser. No. 62/544,417 entitled “PRECODING REFERENCE SIGNALSFOR UPLINK TRANSMISSION WITH DOWNLINK INTERFERENCE INFORMATION,” whichwas filed Aug. 11, 2017. Each of the aforementioned applications isherein incorporated by reference in its entirety.

FIELD

The present disclosure relates generally to communication systems, andmore particularly, to methods and apparatus relating to precodingreference signals for uplink transmission with downlink interferenceinformation.

BACKGROUND

Wireless communication systems are widely deployed to provide varioustelecommunication services such as telephony, video, data, messaging,and broadcasts. Typical wireless communication systems may employmultiple-access technologies capable of supporting communication withmultiple users by sharing available system resources (e.g., bandwidth,transmit power). Examples of such multiple-access technologies includeLong Term Evolution (LTE) systems, code division multiple access (CDMA)systems, time division multiple access (TDMA) systems, frequencydivision multiple access (FDMA) systems, orthogonal frequency divisionmultiple access (OFDMA) systems, single-carrier frequency divisionmultiple access (SC-FDMA) systems, and time division synchronous codedivision multiple access (TD-SCDMA) systems.

In some examples, a wireless multiple-access communication system mayinclude a number of base stations, each simultaneously supportingcommunication for multiple communication devices, otherwise known asuser equipment (UEs). In LTE or LTE-A network, a set of one or more basestations may define an eNodeB (eNB). In other examples (e.g., in a nextgeneration or 5G network), a wireless multiple access communicationsystem may include a number of distributed units (DUs) (e.g., edge units(EUs), edge nodes (ENs), radio heads (RHs), smart radio heads (SRHs),transmission reception points (TRPs), etc.) in communication with anumber of central units (CUs) (e.g., central nodes (CNs), access nodecontrollers (ANCs), etc.), where a set of one or more distributed units,in communication with a central unit, may define an access node (e.g., anew radio base station (NR BS), a new radio node-B (NR NB), a networknode, 5G NB, eNB, etc.). A base station or DU may communicate with a setof UEs on downlink channels (e.g., for transmissions from a base stationor to a UE) and uplink channels (e.g., for transmissions from a UE to abase station or distributed unit).

These multiple access technologies have been adopted in varioustelecommunication standards to provide a common protocol that enablesdifferent wireless devices to communicate on a municipal, national,regional, and even global level. An example of an emergingtelecommunication standard is new radio (NR), for example, 5G radioaccess. NR is a set of enhancements to the LTE mobile standardpromulgated by Third Generation Partnership Project (3GPP). It isdesigned to better support mobile broadband Internet access by improvingspectral efficiency, lowering costs, improving services, making use ofnew spectrum, and better integrating with other open standards usingOFDMA with a cyclic prefix (CP) on the downlink (DL) and on the uplink(UL) as well as support beamforming, multiple-input multiple-output(MIMO) antenna technology, and carrier aggregation.

However, as the demand for mobile broadband access continues toincrease, there exists a desire for further improvements in NRtechnology. Preferably, these improvements should be applicable to othermulti-access technologies and the telecommunication standards thatemploy these technologies.

BRIEF SUMMARY

The systems, methods, and devices of the disclosure each have severalaspects, no single one of which is solely responsible for its desirableattributes. Without limiting the scope of this disclosure as expressedby the claims which follow, some features will now be discussed briefly.After considering this discussion, and particularly after reading thesection entitled “Detailed Description” one will understand how thefeatures of this disclosure provide advantages that include improvedcommunications between access points and stations in a wireless network.

Certain aspects provide a method for wireless communications by a userequipment (UE). The method generally includes receiving, from a basestation, one or more signals for use in estimating channel quality for adownlink between the base station and the UE, determining a firstfrequency resource and a second frequency resource from a frequency bandallocated for transmitting a reference signal (RS), computing a firstdownlink channel quality estimate for the first frequency resource usingthe one or more signals, transmitting a first RS precoded using thefirst downlink channel quality estimate, computing a second downlinkchannel quality estimate for the second frequency resource using the oneor more signals, and transmitting a second RS precoded using the seconddownlink channel quality estimate.

Also described herein are embodiments of an apparatus comprising anon-transitory memory comprising executable instructions and a processorin data communication with the memory and configured to execute theinstructions to cause the apparatus to receive, from a base station, oneor more signals for use in estimating channel quality for a downlinkbetween the base station and the apparatus, determine a first frequencyresource and a second frequency resource from a frequency band allocatedfor transmitting a reference signal (RS), compute a first downlinkchannel quality estimate for the first frequency resource using the oneor more signals, transmit a first RS precoded using the first downlinkchannel quality estimate, compute a second downlink channel qualityestimate for the second frequency resource using the one or moresignals, and transmit a second RS precoded using the second downlinkchannel quality estimate.

Also described herein are embodiments of an apparatus means forreceiving, from a base station, one or more signals for use inestimating channel quality for a downlink between the base station andthe apparatus, means for determining a first frequency resource and asecond frequency resource from a frequency band allocated fortransmitting a reference signal (RS), means for computing a firstdownlink channel quality estimate for the first frequency resource usingthe one or more signals, means for transmitting a first RS precodedusing the first downlink channel quality estimate, means for computing asecond downlink channel quality estimate for the second frequencyresource using the one or more signals, and means for transmitting asecond RS precoded using the second downlink channel quality estimate.

Also described herein are embodiments of a non-transitory computerreadable medium comprising instructions to be executed in an apparatus,wherein the instructions when executed in the apparatus perform amethod, where the method includes receiving, from a base station, one ormore signals for use in estimating channel quality for a downlinkbetween the base station and a UE, determining a first frequencyresource and a second frequency resource from a frequency band allocatedfor transmitting a reference signal (RS), computing a first downlinkchannel quality estimate for the first frequency resource using the oneor more signals, transmitting a first RS precoded using the firstdownlink channel quality estimate, computing a second downlink channelquality estimate for the second frequency resource using the one or moresignals, and transmitting a second RS precoded using the second downlinkchannel quality estimate.

Aspects generally include methods, apparatus, systems, computer readablemediums, and processing systems, as substantially described herein withreference to and as illustrated by the accompanying drawings.

To the accomplishment of the foregoing and related ends, the one or moreaspects comprise the features hereinafter fully described andparticularly pointed out in the claims. The following description andthe annexed drawings set forth in detail certain illustrative featuresof the one or more aspects. These features are indicative, however, ofbut a few of the various ways in which the principles of various aspectsmay be employed, and this description is intended to include all suchaspects and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description,briefly summarized above, may be had by reference to aspects, some ofwhich are illustrated in the appended drawings. It is to be noted,however, that the appended drawings illustrate only certain typicalaspects of this disclosure and are therefore not to be consideredlimiting of its scope, for the description may admit to other equallyeffective aspects.

FIG. 1 is a block diagram conceptually illustrating an exampletelecommunications system, in accordance with certain aspects of thepresent disclosure.

FIG. 2 is a block diagram illustrating an example logical architectureof a distributed RAN, in accordance with certain aspects of the presentdisclosure.

FIG. 3 is a diagram illustrating an example physical architecture of adistributed RAN, in accordance with certain aspects of the presentdisclosure.

FIG. 4 is a block diagram conceptually illustrating a design of anexample BS and user equipment (UE), in accordance with certain aspectsof the present disclosure.

FIG. 5 is a diagram showing examples for implementing a communicationprotocol stack, in accordance with certain aspects of the presentdisclosure.

FIG. 6 illustrates an example of a DL-centric subframe, in accordancewith certain aspects of the present disclosure.

FIG. 7 illustrates an example of an UL-centric subframe, in accordancewith certain aspects of the present disclosure.

FIG. 8 illustrates example operations of wireless communications for useby a UE, in accordance with certain aspects of the present disclosure.

FIG. 8A illustrates a wireless communications device that may includevarious components configured to perform operations for the techniquesdisclosed herein, such as one or more of the operations illustrated inFIG. 8.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in one aspectmay be beneficially utilized on other aspects without specificrecitation.

DETAILED DESCRIPTION

Aspects of the present disclosure relate to methods and apparatusrelating to precoding reference signals for uplink transmission withdownlink interference information.

Aspects of the present disclosure provide apparatus, methods, processingsystems, and computer readable mediums for new radio (NR) (new radioaccess technology or 5G technology).

NR may support various wireless communication services, such as Enhancedmobile broadband (eMBB) targeting wide bandwidth (e.g. 80 MHz beyond),millimeter wave (mmW) targeting high carrier frequency (e.g. 60 GHz),massive MTC (mMTC) targeting non-backward compatible MTC techniques,and/or mission critical targeting ultra-reliable low latencycommunications (URLLC). These services may include latency andreliability requirements. These services may also have differenttransmission time intervals (TTI) to meet respective quality of service(QoS) requirements. In addition, these services may co-exist in the samesubframe.

A user equipment (UE), such as one conforming to the NR wirelesscommunications standards, may transmit one or more sounding referencesignals (SRS) on the uplink to a base station (e.g., gNB) to enable thebase station to estimate the uplink channel quality over a portion ofthe channel bandwidth over which the SRS is transmitted by the UE.Further, the UE may separately transmit information indicative of anestimate of downlink channel quality to the base station. For example,after receiving a reference signal (e.g., CRS (cell-specific referencesignal), CSI-RS (channel state information-reference signal), ZP-CSI-RS(zero-power CSI-RS), etc.), the UE may estimate the downlink channelquality based on the reference signal and transmit information back tothe BS that is indicative of such an estimation. In some cases, in orderto utilize less resources on the uplink for transmitting SRS andinformation indicative of the estimate of downlink channel quality tothe base station, in certain aspects, the SRS may be coded (e.g.,precoded) with information indicative of the estimate of downlinkchannel quality. An example of information indicative of the estimate ofdownlink channel quality is an R_(nn) matrix, which is the interferencecovariance matrix across receive antennas at the UE based on the signalsreceived by the UE on the downlink.

For example, the R_(nn) matrix may be applied by a pre-coder to the SRSprior to the SRS transmission. In some cases, to pre-code the SRS withinformation indicative of the estimate of downlink channel quality(e.g., R_(nn) matrix), a pre-whitened SRS is used. A pre-whitened SRS isan example of when a pre-coder applies an operation, such assqrt(inv(R_(nn))), to the SRS, in which case the R_(nn) may first needto be computed over the entire bandwidth over which SRS is transmittedand, then, the square root of the inverse of the R_(nn) may be appliedto the SRS sequence. However, pre-whitening the SRS involves an extralevel of computational complexity including computing R_(nn) andapplying the inverse of R_(nn) to the SRS sequence, which may taketime/compute cycles to process.

Accordingly, certain embodiments discussed herein relate to amulti-stage R_(nn) feedback mechanism whereby the UE computes an R_(nn)over only a portion (e.g., subband) of the frequency band (e.g.,bandwidth) used for transmitting a SRS transmission. By implementing theembodiments described herein, less time and compute cycles are used whenSRS is pre-coded with information indicative of the estimate of downlinkchannel quality (e.g., R_(nn) matrix).

The following description provides examples, and is not limiting of thescope, applicability, or examples set forth in the claims. Changes maybe made in the function and arrangement of elements discussed withoutdeparting from the scope of the disclosure. Various examples may omit,substitute, or add various procedures or components as appropriate. Forinstance, the methods described may be performed in an order differentfrom that described, and various steps may be added, omitted, orcombined. Also, features described with respect to some examples may becombined in some other examples. For example, an apparatus may beimplemented or a method may be practiced using any number of the aspectsset forth herein. In addition, the scope of the disclosure is intendedto cover such an apparatus or method which is practiced using otherstructure, functionality, or structure and functionality in addition toor other than the various aspects of the disclosure set forth herein. Itshould be understood that any aspect of the disclosure disclosed hereinmay be embodied by one or more elements of a claim. The word “exemplary”is used herein to mean “serving as an example, instance, orillustration.” Any aspect described herein as “exemplary” is notnecessarily to be construed as preferred or advantageous over otheraspects.

The techniques described herein may be used for various wirelesscommunication networks such as LTE, CDMA, TDMA, FDMA, OFDMA, SC-FDMA andother networks. The terms “network” and “system” are often usedinterchangeably. A CDMA network may implement a radio technology such asUniversal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includesWideband CDMA (WCDMA) and other variants of CDMA. cdma2000 coversIS-2000, IS-95 and IS-856 standards. A TDMA network may implement aradio technology such as Global System for Mobile Communications (GSM).An OFDMA network may implement a radio technology such as NR (e.g. 5GRA), Evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDMA, etc. UTRA andE-UTRA are part of Universal Mobile Telecommunication System (UMTS). NRis an emerging wireless communications technology under development inconjunction with the 5G Technology Forum (5GTF). 3GPP Long TermEvolution (LTE) and LTE-Advanced (LTE-A) are releases of UMTS that useE-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are described indocuments from an organization named “3rd Generation PartnershipProject” (3GPP). cdma2000 and UMB are described in documents from anorganization named “3rd Generation Partnership Project 2” (3GPP2). Thetechniques described herein may be used for the wireless networks andradio technologies mentioned above as well as other wireless networksand radio technologies. For clarity, while aspects may be describedherein using terminology commonly associated with 3G and/or 4G wirelesstechnologies, aspects of the present disclosure can be applied in othergeneration-based communication systems, such as 5G and later, includingNR technologies.

Example Wireless Communications System

FIG. 1 illustrates an example wireless network 100, such as a new radio(NR) or 5G network, in which aspects of the present disclosure may beperformed. For example, base station (BS) 110 may transmit one or moresignals to a user equipment (UE) 120 for use in computing a downlinkchannel quality estimate for a downlink of the UE, based on which the UE120 may code one or more reference signals with downlink channel qualitythat is computed and transmit the one or more coded reference signalsback to the BS 110 (e.g., operations 800 of FIG. 8).

As illustrated in FIG. 1, the wireless network 100 may include a numberof BSs 110 and other network entities. A BS may be a station thatcommunicates with UEs. Each BS 110 may provide communication coveragefor a particular geographic area. In 3GPP, the term “cell” can refer toa coverage area of a Node B and/or a Node B subsystem serving thiscoverage area, depending on the context in which the term is used. In NRsystems, the term “cell” and eNB, Node B, 5G NB, AP, NR BS, NR BS, orTRP may be interchangeable. In some examples, a cell may not necessarilybe stationary, and the geographic area of the cell may move according tothe location of a mobile base station. In some examples, the basestations may be interconnected to one another and/or to one or moreother base stations or network nodes (not shown) in the wireless network100 through various types of backhaul interfaces such as a directphysical connection, a virtual network, or the like using any suitabletransport network.

In general, any number of wireless networks may be deployed in a givengeographic area. Each wireless network may support a particular radioaccess technology (RAT) and may operate on one or more frequencies. ARAT may also be referred to as a radio technology, an air interface,etc. A frequency may also be referred to as a carrier, a frequencychannel, etc. Each frequency may support a single RAT in a givengeographic area in order to avoid interference between wireless networksof different RATs. In some cases, NR or 5G RAT networks may be deployed.

A BS may provide communication coverage for a macro cell, a pico cell, afemto cell, and/or other types of cell. A macro cell may cover arelatively large geographic area (e.g., several kilometers in radius)and may allow unrestricted access by UEs with service subscription. Apico cell may cover a relatively small geographic area and may allowunrestricted access by UEs with service subscription. A femto cell maycover a relatively small geographic area (e.g., a home) and may allowrestricted access by UEs having association with the femto cell (e.g.,UEs in a Closed Subscriber Group (CSG), UEs for users in the home,etc.). A BS for a macro cell may be referred to as a macro BS. A BS fora pico cell may be referred to as a pico BS. A BS for a femto cell maybe referred to as a femto BS or a home BS. In the example shown in FIG.1, the BSs 110 a, 110 b and 110 c may be macro BSs for the macro cells102 a, 102 b and 102 c, respectively. The BS 110 x may be a pico BS fora pico cell 102 x. The BSs 110 y and 110 z may be femto BS for the femtocells 102 y and 102 z, respectively. ABS may support one or multiple(e.g., three) cells.

The wireless network 100 may also include relay stations. A relaystation is a station that receives a transmission of data and/or otherinformation from an upstream station (e.g., a BS or a UE) and sends atransmission of the data and/or other information to a downstreamstation (e.g., a UE or a BS). A relay station may also be a UE thatrelays transmissions for other UEs. In the example shown in FIG. 1, arelay station 110 r may communicate with the BS 110 a and a UE 120 r inorder to facilitate communication between the BS 110 a and the UE 120 r.A relay station may also be referred to as a relay BS, a relay, etc.

The wireless network 100 may be a heterogeneous network that includesBSs of different types, e.g., macro BS, pico BS, femto BS, relays, etc.These different types of BSs may have different transmit power levels,different coverage areas, and different impact on interference in thewireless network 100. For example, macro BS may have a high transmitpower level (e.g., 20 Watts) whereas pico BS, femto BS, and relays mayhave a lower transmit power level (e.g., 1 Watt).

The wireless network 100 may support synchronous or asynchronousoperation. For synchronous operation, the BSs may have similar frametiming, and transmissions from different BSs may be approximatelyaligned in time. For asynchronous operation, the BSs may have differentframe timing, and transmissions from different BSs may not be aligned intime. The techniques described herein may be used for both synchronousand asynchronous operation.

A network controller 130 may be coupled to a set of BSs and providecoordination and control for these BSs. The network controller 130 maycommunicate with the BSs 110 via a backhaul. The BSs 110 may alsocommunicate with one another, e.g., directly or indirectly via wirelessor wireline backhaul.

The UEs 120 (e.g., 120 x, 120 y, etc.) may be dispersed throughout thewireless network 100, and each UE may be stationary or mobile. A UE mayalso be referred to as a mobile station, a terminal, an access terminal,a subscriber unit, a station, a Customer Premises Equipment (CPE), acellular phone, a smart phone, a personal digital assistant (PDA), awireless modem, a wireless communication device, a handheld device, alaptop computer, a cordless phone, a wireless local loop (WLL) station,a tablet, a camera, a gaming device, a netbook, a smartbook, anultrabook, a medical device or medical equipment, a biometricsensor/device, a wearable device such as a smart watch, smart clothing,smart glasses, a smart wrist band, smart jewelry (e.g., a smart ring, asmart bracelet, etc.), an entertainment device (e.g., a music device, avideo device, a satellite radio, etc.), a vehicular component or sensor,a smart meter/sensor, industrial manufacturing equipment, a globalpositioning system device, or any other suitable device that isconfigured to communicate via a wireless or wired medium. Some UEs maybe considered evolved or machine-type communication (MTC) devices orevolved MTC (eMTC) devices. MTC and eMTC UEs include, for example,robots, drones, remote devices, sensors, meters, monitors, locationtags, etc., that may communicate with a BS, another device (e.g., remotedevice), or some other entity. A wireless node may provide, for example,connectivity for or to a network (e.g., a wide area network such asInternet or a cellular network) via a wired or wireless communicationlink. Some UEs may be considered Internet-of-Things (IoT) devices. InFIG. 1, a solid line with double arrows indicates desired transmissionsbetween a UE and a serving BS, which is a BS designated to serve the UEon the downlink and/or uplink. A dashed line with double arrowsindicates interfering transmissions between a UE and a BS.

Certain wireless networks (e.g., LTE) utilize orthogonal frequencydivision multiplexing (OFDM) on the downlink and single-carrierfrequency division multiplexing (SC-FDM) on the uplink. OFDM and SC-FDMpartition the system bandwidth into multiple (K) orthogonal subcarriers,which are also commonly referred to as tones, bins, etc. Each subcarriermay be modulated with data. In general, modulation symbols are sent inthe frequency domain with OFDM and in the time domain with SC-FDM. Thespacing between adjacent subcarriers may be fixed, and the total numberof subcarriers (K) may be dependent on the system bandwidth. Forexample, the spacing of the subcarriers may be 15 kHz and the minimumresource allocation (called a ‘resource block’) may be 12 subcarriers(or 180 kHz). Consequently, the nominal FFT size may be equal to 128,256, 512, 1024 or 2048 for system bandwidth of 1.25, 2.5, 5, 10 or 20megahertz (MHz), respectively. The system bandwidth may also bepartitioned into subbands. For example, a subband may cover 1.08 MHz(i.e., 6 resource blocks), and there may be 1, 2, 4, 8 or 16 subbandsfor system bandwidth of 1.25, 2.5, 5, 10 or 20 MHz, respectively.

While aspects of the examples described herein may be associated withLTE technologies, aspects of the present disclosure may be applicablewith other wireless communications systems, such as NR. NR may utilizeOFDM with a CP on the uplink and downlink and include support forhalf-duplex operation using time division duplex (TDD). A singlecomponent carrier bandwidth of 100 MHz may be supported. NR resourceblocks may span 12 sub-carriers with a sub-carrier bandwidth of 75 kHzover a 0.1 ms duration. Each radio frame may consist of 50 subframeswith a length of 10 ms. Consequently, each subframe may have a length of0.2 ms. Each subframe may indicate a link direction (i.e., DL or UL) fordata transmission and the link direction for each subframe may bedynamically switched. Each subframe may include DL/UL data as well asDL/UL control data. UL and DL subframes for NR may be as described inmore detail below. Beamforming may be supported and beam direction maybe dynamically configured. MIMO transmissions with precoding may also besupported. MIMO configurations in the DL may support up to 8 transmitantennas with multi-layer DL transmissions up to 8 streams and up to 2streams per UE. Multi-layer transmissions with up to 2 streams per UEmay be supported. Aggregation of multiple cells may be supported with upto 8 serving cells. Alternatively, NR may support a different airinterface, other than an OFDM-based. NR networks may include entitiessuch CUs and/or DUs.

In some examples, access to the air interface may be scheduled, whereina scheduling entity (e.g., a base station) allocates resources forcommunication among some or all devices and equipment within its servicearea or cell. Within the present disclosure, as discussed further below,the scheduling entity may be responsible for scheduling, assigning,reconfiguring, and releasing resources for one or more subordinateentities. That is, for scheduled communication, subordinate entitiesutilize resources allocated by the scheduling entity. Base stations arenot the only entities that may function as a scheduling entity. That is,in some examples, a UE may function as a scheduling entity, schedulingresources for one or more subordinate entities (e.g., one or more otherUEs). In this example, the UE is functioning as a scheduling entity, andother UEs utilize resources scheduled by the UE for wirelesscommunication. A UE may function as a scheduling entity in apeer-to-peer (P2P) network, and/or in a mesh network. In a mesh networkexample, UEs may optionally communicate directly with one another inaddition to communicating with the scheduling entity.

Thus, in a wireless communication network with a scheduled access totime-frequency resources and having a cellular configuration, a P2Pconfiguration, and a mesh configuration, a scheduling entity and one ormore subordinate entities may communicate utilizing the scheduledresources.

As noted above, a RAN may include a CU and DUs. A NR BS (e.g., eNB, 5GNode B, Node B, transmission reception point (TRP), access point (AP))may correspond to one or multiple BSs. NR cells can be configured asaccess cell (ACells) or data only cells (DCells). For example, the RAN(e.g., a central unit or distributed unit) can configure the cells.DCells may be cells used for carrier aggregation or dual connectivity,but not used for initial access, cell selection/reselection, orhandover. In some cases DCells may not transmit synchronizationsignals—in some case cases DCells may transmit SS. NR BSs may transmitdownlink signals to UEs indicating the cell type. Based on the cell typeindication, the UE may communicate with the NR BS. For example, the UEmay determine NR BSs to consider for cell selection, access, handover,and/or measurement based on the indicated cell type.

FIG. 2 illustrates an example logical architecture of a distributedradio access network (RAN) 200, which may be implemented in the wirelesscommunication system illustrated in FIG. 1. A 5G access node 206 mayinclude an access node controller (ANC) 202. The ANC may be a centralunit (CU) of the distributed RAN 200. The backhaul interface to the nextgeneration core network (NG-CN) 204 may terminate at the ANC. Thebackhaul interface to neighboring next generation access nodes (NG-ANs)may terminate at the ANC. The ANC may include one or more TRPs 208(which may also be referred to as BSs, NR BSs, Node Bs, 5G NBs, APs, orsome other term). As described above, a TRP may be used interchangeablywith “cell.”

The TRPs 208 may be a DU. The TRPs may be connected to one ANC (ANC 202)or more than one ANC (not illustrated). For example, for RAN sharing,radio as a service (RaaS), and service specific AND deployments, the TRPmay be connected to more than one ANC. A TRP may include one or moreantenna ports. The TRPs may be configured to individually (e.g., dynamicselection) or jointly (e.g., joint transmission) serve traffic to a UE.

The local architecture 200 may be used to illustrate fronthauldefinition. The architecture may be defined that support fronthaulingsolutions across different deployment types. For example, thearchitecture may be based on transmit network capabilities (e.g.,bandwidth, latency, and/or jitter).

The architecture may share features and/or components with LTE.According to aspects, the next generation AN (NG-AN) 210 may supportdual connectivity with NR. The NG-AN may share a common fronthaul forLTE and NR.

The architecture may enable cooperation between and among TRPs 208. Forexample, cooperation may be preset within a TRP and/or across TRPs viathe ANC 202. According to aspects, no inter-TRP interface may beneeded/present.

According to aspects, a dynamic configuration of split logical functionsmay be present within the architecture 200. As will be described in moredetail with reference to FIG. 5, the Radio Resource Control (RRC) layer,Packet Data Convergence Protocol (PDCP) layer, Radio Link Control (RLC)layer, Medium Access Control (MAC) layer, and a Physical (PHY) layersmay be adaptably placed at the DU or CU (e.g., TRP or ANC,respectively). According to certain aspects, a BS may include a centralunit (CU) (e.g., ANC 202) and/or one or more distributed units (e.g.,one or more TRPs 208).

FIG. 3 illustrates an example physical architecture of a distributed RAN300, according to aspects of the present disclosure. A centralized corenetwork unit (C-CU) 302 may host core network functions. The C-CU may becentrally deployed. C-CU functionality may be offloaded (e.g., toadvanced wireless services (AWS)), in an effort to handle peak capacity.

A centralized RAN unit (C-RU) 304 may host one or more ANC functions.Optionally, the C-RU may host core network functions locally. The C-RUmay have distributed deployment. The C-RU may be closer to the networkedge.

A DU 306 may host one or more TRPs (edge node (EN), an edge unit (EU), aradio head (RH), a smart radio head (SRH), or the like). The DU may belocated at edges of the network with radio frequency (RF) functionality.

FIG. 4 illustrates example components of the BS 110 and UE 120illustrated in FIG. 1, which may be used to implement aspects of thepresent disclosure. As described above, the BS may include a TRP. One ormore components of the BS 110 and UE 120 may be used to practice aspectsof the present disclosure. For example, antennas 452, Tx/Rx 222,processors 466, 458, 464, and/or controller/processor 480 of the UE 120and/or antennas 434, processors 460, 420, 438, and/orcontroller/processor 440 of the BS 110 may be used to perform theoperations described herein (e.g., operations 800 of FIG. 8).

FIG. 4 shows a block diagram of a design of a BS 110 and a UE 120, whichmay be one of the BSs and one of the UEs in FIG. 1. For a restrictedassociation scenario, the base station 110 may be the macro BS 110 c inFIG. 1, and the UE 120 may be the UE 120 y. The base station 110 mayalso be a base station of some other type. The base station 110 may beequipped with antennas 434 a through 434 t, and the UE 120 may beequipped with antennas 452 a through 452 r.

At the base station 110, a transmit processor 420 may receive data froma data source 412 and control information from a controller/processor440. The control information may be for the Physical Broadcast Channel(PBCH), Physical Control Format Indicator Channel (PCFICH), PhysicalHybrid ARQ Indicator Channel (PHICH), Physical Downlink Control Channel(PDCCH), etc. The data may be for the Physical Downlink Shared Channel(PDSCH), etc. The processor 420 may process (e.g., encode and symbolmap) the data and control information to obtain data symbols and controlsymbols, respectively. The processor 420 may also generate referencesymbols, e.g., for the PSS, SSS, and cell-specific reference signal. Atransmit (TX) multiple-input multiple-output (MIMO) processor 430 mayperform spatial processing (e.g., precoding) on the data symbols, thecontrol symbols, and/or the reference symbols, if applicable, and mayprovide output symbol streams to the modulators (MODs) 432 a through 432t. For example, the TX MIMO processor 430 may perform certain aspectsdescribed herein for RS multiplexing. Each modulator 432 may process arespective output symbol stream (e.g., for OFDM, etc.) to obtain anoutput sample stream. Each modulator 432 may further process (e.g.,convert to analog, amplify, filter, and upconvert) the output samplestream to obtain a downlink signal. Downlink signals from modulators 432a through 432 t may be transmitted via the antennas 434 a through 434 t,respectively.

At the UE 120, the antennas 452 a through 452 r may receive the downlinksignals from the base station 110 and may provide received signals tothe demodulators (DEMODs) 454 a through 454 r, respectively. Eachdemodulator 454 may condition (e.g., filter, amplify, downconvert, anddigitize) a respective received signal to obtain input samples. Eachdemodulator 454 may further process the input samples (e.g., for OFDM,etc.) to obtain received symbols. A MIMO detector 456 may obtainreceived symbols from all the demodulators 454 a through 454 r, performMIMO detection on the received symbols if applicable, and providedetected symbols. For example, MIMO detector 456 may provide detected RStransmitted using techniques described herein. A receive processor 458may process (e.g., demodulate, deinterleave, and decode) the detectedsymbols, provide decoded data for the UE 120 to a data sink 460, andprovide decoded control information to a controller/processor 480.According to one or more cases, CoMP aspects can include providing theantennas, as well as some Tx/Rx functionalities, such that they residein distributed units. For example, some Tx/Rx processings can be done inthe central unit, while other processing can be done at the distributedunits. For example, in accordance with one or more aspects as shown inthe diagram, the BS mod/demod 432 may be in the distributed units.

On the uplink, at the UE 120, a transmit processor 464 may receive andprocess data (e.g., for the Physical Uplink Shared Channel (PUSCH)) froma data source 462 and control information (e.g., for the Physical UplinkControl Channel (PUCCH) from the controller/processor 480. The transmitprocessor 464 may also generate reference symbols for a referencesignal. The symbols from the transmit processor 464 may be precoded by aTX MIMO processor 466 if applicable, further processed by thedemodulators 454 a through 454 r (e.g., for SC-FDM, etc.), andtransmitted to the base station 110. At the BS 110, the uplink signalsfrom the UE 120 may be received by the antennas 434, processed by themodulators 432, detected by a MIMO detector 436 if applicable, andfurther processed by a receive processor 438 to obtain decoded data andcontrol information sent by the UE 120. The receive processor 438 mayprovide the decoded data to a data sink 439 and the decoded controlinformation to the controller/processor 440.

The controllers/processors 440 and 480 may direct the operation at thebase station 110 and the UE 120, respectively. The processor 440 and/orother processors and modules at the base station 110 may perform ordirect, e.g., the execution of certain processes for the techniquesdescribed herein. The processor 480 and/or other processors and modulesat the UE 120 may also perform or direct, e.g., the execution of thefunctional blocks illustrated in FIG. 8, and/or other processes for thetechniques described herein. The memories 442 and 482 may store data andprogram codes for the BS 110 and the UE 120, respectively. A scheduler444 may schedule UEs for data transmission on the downlink and/oruplink.

FIG. 5 illustrates a diagram 500 showing examples for implementing acommunications protocol stack, according to aspects of the presentdisclosure. The illustrated communications protocol stacks may beimplemented by devices operating in a in a 5G system (e.g., a systemthat supports uplink-based mobility). Diagram 500 illustrates acommunications protocol stack including a Radio Resource Control (RRC)layer 510, a Packet Data Convergence Protocol (PDCP) layer 515, a RadioLink Control (RLC) layer 520, a Medium Access Control (MAC) layer 525,and a Physical (PHY) layer 530. In various examples the layers of aprotocol stack may be implemented as separate modules of software,portions of a processor or ASIC, portions of non-collocated devicesconnected by a communications link, or various combinations thereof.Collocated and non-collocated implementations may be used, for example,in a protocol stack for a network access device (e.g., ANs, CUs, and/orDUs) or a UE.

A first option 505-a shows a split implementation of a protocol stack,in which implementation of the protocol stack is split between acentralized network access device (e.g., an ANC 202 in FIG. 2) anddistributed network access device (e.g., DU 208 in FIG. 2). In the firstoption 505-a, an RRC layer 510 and a PDCP layer 515 may be implementedby the central unit, and an RLC layer 520, a MAC layer 525, and a PHYlayer 530 may be implemented by the DU. In various examples the CU andthe DU may be collocated or non-collocated. The first option 505-a maybe useful in a macro cell, micro cell, or pico cell deployment.

A second option 505-b shows a unified implementation of a protocolstack, in which the protocol stack is implemented in a single networkaccess device (e.g., access node (AN), new radio base station (NR BS), anew radio Node-B (NR NB), a network node (NN), or the like.). In thesecond option, the RRC layer 510, the PDCP layer 515, the RLC layer 520,the MAC layer 525, and the PHY layer 530 may each be implemented by theAN. The second option 505-b may be useful in a femto cell deployment.

Regardless of whether a network access device implements part or all ofa protocol stack, a UE may implement an entire protocol stack (e.g., theRRC layer 510, the PDCP layer 515, the RLC layer 520, the MAC layer 525,and the PHY layer 530).

FIG. 6 is a diagram 600 showing an example of a DL-centric subframe. TheDL-centric subframe may include a control portion 602. The controlportion 602 may exist in the initial or beginning portion of theDL-centric subframe. The control portion 602 may include variousscheduling information and/or control information corresponding tovarious portions of the DL-centric subframe. In some configurations, thecontrol portion 602 may be a physical DL control channel (PDCCH), asindicated in FIG. 6. The DL-centric subframe may also include a DL dataportion 604. The DL data portion 604 may sometimes be referred to as thepayload of the DL-centric subframe. The DL data portion 604 may includethe communication resources utilized to communicate DL data from thescheduling entity (e.g., UE or BS) to the subordinate entity (e.g., UE).In some configurations, the DL data portion 604 may be a physical DLshared channel (PDSCH).

The DL-centric subframe may also include a common UL portion 606. Thecommon UL portion 606 may sometimes be referred to as an UL burst, acommon UL burst, and/or various other suitable terms. The common ULportion 606 may include feedback information corresponding to variousother portions of the DL-centric subframe. For example, the common ULportion 606 may include feedback information corresponding to thecontrol portion 602. Non-limiting examples of feedback information mayinclude an ACK signal, a NACK signal, a HARQ indicator, and/or variousother suitable types of information. The common UL portion 606 mayinclude additional or alternative information, such as informationpertaining to random access channel (RACH) procedures, schedulingrequests (SRs), and various other suitable types of information. Asillustrated in FIG. 6, the end of the DL data portion 604 may beseparated in time from the beginning of the common UL portion 606. Thistime separation may sometimes be referred to as a gap, a guard period, aguard interval, and/or various other suitable terms. This separationprovides time for the switch-over from DL communication (e.g., receptionoperation by the subordinate entity (e.g., UE)) to UL communication(e.g., transmission by the subordinate entity (e.g., UE)). One ofordinary skill in the art will understand that the foregoing is merelyone example of a DL-centric subframe and alternative structures havingsimilar features may exist without necessarily deviating from theaspects described herein.

FIG. 7 is a diagram 700 showing an example of an UL-centric subframe.The UL-centric subframe may include a control portion 702. The controlportion 702 may exist in the initial or beginning portion of theUL-centric subframe. The control portion 702 in FIG. 7 may be similar tothe control portion described above with reference to FIG. 6. TheUL-centric subframe may also include an UL data portion 704. The UL dataportion 704 may sometimes be referred to as the payload of theUL-centric subframe. The UL data portion may refer to the communicationresources utilized to communicate UL data from the subordinate entity(e.g., UE) to the scheduling entity (e.g., UE or BS). In someconfigurations, the control portion 702 may be a physical DL controlchannel (PDCCH).

As illustrated in FIG. 7, the end of the control portion 702 may beseparated in time from the beginning of the UL data portion 704. Thistime separation may sometimes be referred to as a gap, guard period,guard interval, and/or various other suitable terms. This separationprovides time for the switch-over from DL communication (e.g., receptionoperation by the scheduling entity) to UL communication (e.g.,transmission by the scheduling entity). The UL-centric subframe may alsoinclude a common UL portion 706. The common UL portion 706 in FIG. 7 maybe similar to the common UL portion 706 described above with referenceto FIG. 7. The common UL portion 706 may additionally or alternativelyinclude information pertaining to channel quality indicator (CQI),sounding reference signals (SRSs), and various other suitable types ofinformation. One of ordinary skill in the art will understand that theforegoing is merely one example of an UL-centric subframe andalternative structures having similar features may exist withoutnecessarily deviating from the aspects described herein.

In some circumstances, two or more subordinate entities (e.g., UEs) maycommunicate with each other using sidelink signals. Real-worldapplications of such sidelink communications may include public safety,proximity services, UE-to-network relaying, vehicle-to-vehicle (V2V)communications, Internet of Everything (IoE) communications, IoTcommunications, mission-critical mesh, and/or various other suitableapplications. Generally, a sidelink signal may refer to a signalcommunicated from one subordinate entity (e.g., UE1) to anothersubordinate entity (e.g., UE2) without relaying that communicationthrough the scheduling entity (e.g., UE or BS), even though thescheduling entity may be utilized for scheduling and/or controlpurposes. In some examples, the sidelink signals may be communicatedusing a licensed spectrum (unlike wireless local area networks, whichtypically use an unlicensed spectrum).

A UE may operate in various radio resource configurations, including aconfiguration associated with transmitting pilots using a dedicated setof resources (e.g., a radio resource control (RRC) dedicated state,etc.) or a configuration associated with transmitting pilots using acommon set of resources (e.g., an RRC common state, etc.). Whenoperating in the RRC dedicated state, the UE may select a dedicated setof resources for transmitting a pilot signal to a network. Whenoperating in the RRC common state, the UE may select a common set ofresources for transmitting a pilot signal to the network. In eithercase, a pilot signal transmitted by the UE may be received by one ormore network access devices, such as an AN, or a DU, or portionsthereof. Each receiving network access device may be configured toreceive and measure pilot signals transmitted on the common set ofresources, and also receive and measure pilot signals transmitted ondedicated sets of resources allocated to the UEs for which the networkaccess device is a member of a monitoring set of network access devicesfor the UE. One or more of the receiving network access devices, or a CUto which receiving network access device(s) transmit the measurements ofthe pilot signals, may use the measurements to identify serving cellsfor the UEs, or to initiate a change of serving cell for one or more ofthe UEs.

Precoding Reference Signals for Uplink Transmissions with DownlinkInterference Information

In some cases, a user equipment (UE), conforming to the NR wirelesscommunications standards, may transmit one or more sounding referencesignals (SRS) on the uplink to a base station (e.g., gNB) to enable thebase station to estimate the uplink channel quality over a portion ofthe channel bandwidth over which the SRS is transmitted by the UE.Further, the UE may separately transmit information indicative of anestimate of downlink channel quality to the base station. For example,the UE may receive signals (CRS (cell-specific reference signal), CSI-RS(channel state information-reference signal), ZP-CSI-RS (zero-powerCSI-RS), etc.) transmitted by the base station on the downlink andcompute an estimate of downlink channel quality based on the receivedsignals. The downlink channel quality estimate may include an estimateof the downlink propagation channel and/or the downlink interference.The estimate of the downlink channel quality assists the base stationscheduler to properly allocate radio resources to the UEs in the cell.

In certain aspects, a UE may transmit SRS and information indicative ofthe estimate of downlink channel quality to the base station separately,thereby utilizing resources (e.g., frequency, time, spatial resources)on the uplink for each. However, in order to utilize less resources onthe uplink for transmitting SRS and information indicative of theestimate of downlink channel quality to the base station, in certainaspects, the SRS may be coded (e.g., precoded) with informationindicative of the estimate of downlink channel quality. The precoded SRSmay be transmitted by the UE on the uplink using the same uplink channelresources used to normally transmit SRS. When SRS is precoded with theestimate of the downlink channel quality, additional uplink channelresources are not needed to separately send the estimate of downlinkchannel quality to the base station. For example, in some cases, the SRSmay be used to carry (e.g., coded with) an R_(nn) matrix, which is theinterference covariance matrix across receive antennas at the UE basedon the signals received by the UE on the downlink. As an example, n maydenote a vector of noise and interference at the UE. Accordingly, anR_(nn) matrix may, for example, be derived by the following formula:

R _(nn) =E{n n ^(H)}, where E{ } denotes an expectation operation anddenotes a Hermitian or conjugate transpose.

In such cases, the Rim matrix may be applied by a pre-coder to the SRSprior to the SRS transmission. Accordingly, in such cases, the basestation receives the pre-coded SRS, which the base station may use tocalculate downlink precoding of signals for transmission by the basestation. A pre-whitened SRS is an example of when a pre-coder applies anoperation, such as sqrt(inv(R_(nn))), to the SRS, in which case theR_(nn) may first need to be computed over the entire bandwidth overwhich SRS is transmitted and, then, the square root of the inverse ofthe R_(nn) may be applied to the SRS sequence. However, pre-whiteningthe SRS involves an extra level of computational complexity includingcomputing R_(nn) and applying the inverse of R_(nn) to the SRS sequence,which may take time/compute cycles to process.

Accordingly, certain embodiments discussed herein relate to amulti-stage R_(nn) feedback mechanism whereby the UE computes an R_(nn)over only a portion (e.g., subband) of the frequency band (e.g.,bandwidth) used for transmitting a SRS transmission. A frequency bandused for transmitting SRS is hereinafter referred to as a “SRS frequencyband.” It should be noted that though certain aspects are discussed withrespect to coding or precoding an SRS transmission with a R_(nn) toconvey both a reference signal and information indicative of downlinkchannel estimates from a UE to a base station on the UL, similartechniques can be used to apply information indicative of a channelestimate to a reference signal that is then transmitted by either the UEon the UL, or the base station on the DL.

FIG. 8 illustrates example operations 800 for wireless communications bya wireless device, according to aspects of the present disclosure. Thewireless device performing operations 800 may be, for example, a UE.Operations 800 begin, at 802, by receiving (e.g., from a base station)one or more signals (CSR, CSI-RS, ZP-CSI-RS, etc.) for use in estimatingdownlink channel quality for a downlink of the UE. At 804, operations800 continue by determining a first frequency resource and a secondfrequency resource of a frequency band allocated for transmitting one ormore reference signals (RS) (e.g., SRS). Here a frequency resource mayrefer to a subband, a bandwidth part, a group of RBs, a subset of RBs ofa subband or a bandwidth part, etc. At 806, operations 800 continue bycomputing a first downlink channel quality estimate (e.g., interferencecovariance matrix (R_(nn))) for the first frequency resource using theone or more signals. At 808, operations 800 continue by transmitting afirst RS precoded using the first downlink channel quality estimate. At810, operations 800 continue by computing a second downlink channelquality estimate for the second frequency resource using the one or moresignals. At 812, operations 800 continue by transmitting a second RSprecoded using the second downlink channel quality estimate.

FIG. 8A illustrates a wireless communications device 800A that mayinclude various components (e.g., corresponding to means-plus-functioncomponents) configured to perform operations for the techniquesdisclosed herein, such as one or more of the operations illustrated inFIG. 8. The communications device 800A includes a processing system 814coupled to a transceiver 812. The transceiver 812 is configured totransmit and receive signals for the communications device 800A via anantenna 813. The processing system 814 may be configured to performprocessing functions for the communications device 800A, such asprocessing signals, etc.

The processing system 814 includes a processor 809 coupled to acomputer-readable medium/memory 811 via a bus 821. In certain aspects,the computer-readable medium/memory 811 is configured to storeinstructions that when executed by processor 809, cause the processor809 to perform one or more of the operations illustrated in FIG. 8, orother operations for performing the various techniques discussed herein.

In certain aspects, the processing system 814 further includes areceiving component 820 for performing one or more of the operationsillustrated at 802 in FIG. 8. Additionally, the processing system 814includes a determining component 822 for performing one or more of theoperations illustrated at 804 in FIG. 8. Further, the processing system814 includes a computing component 824 for performing one or more of theoperations illustrated at 806 in FIG. 8. Also, the processing system 814includes a transmitting component 826 for performing one or more of theoperations illustrated at 808 in FIG. 8. Also, the processing system 814includes a computing component 828 for performing one or more of theoperations illustrated at 810 in FIG. 8. Also, the processing system 814includes a transmitting component 830 for performing one or more of theoperations illustrated at 810 in FIG. 8.

The receiving component 820, the determining component 822, thecomputing component 824, the transmitting component 826, the computingcomponent 828, and the transmitting component 830, may be coupled to theprocessor 809 via bus 821. In certain aspects, receiving component 820,the determining component 822, the computing component 824, thetransmitting component 826, the computing component 828, and thetransmitting component 830 may be hardware circuits. In certain aspects,receiving component 820, the determining component 822, the computingcomponent 824, the transmitting component 826, the computing component828, and the transmitting component 830 may be software components thatare executed and run on processor 809.

As described above, in some embodiments, a R_(nn) may be computed onlyover a portion of the frequency band (e.g., a portion of the resourceblocks (RBs), a portion of the bandwidth, etc.) over which SRS istransmitted. As an example, the R_(nn) may be computed for a sub-band, abandwidth-part, or a group of RBs that is a subset of the RBs used totransmit SRS. In some embodiments, the group of RBs may be a set ofcontiguous RBs, or a sub-sampling of a set of contiguous RBs (e.g.,every first, second, third, etc. RB, resource block group (RBG), orphysical resource block group (PRG)).

Since the base station receives a R_(nn) that is computed only over aportion of the SRS frequency band, the base station may not have anaccurate estimate of downlink channel quality over the portions of thefrequency band for which R_(nn) was not computed and coded into the SRS.However, in certain aspects, the downlink channel quality over oneportion of a frequency band may be used as an estimate of the downlinkchannel quality over another portion of a frequency band. The estimatemay be more accurate for portions of a frequency band that are closer infrequency, in certain aspects, or that are known to have similarinterference characteristics (e.g., a neighboring base station is knownto communicate in the same channel on both portions of the frequencyband).

In certain aspects, to further provide more accurate estimates ofdownlink channel quality over the portions of the frequency band forwhich R_(nn) was not computed and coded into a first transmitted SRS, insome embodiments, subsequent R_(nn) matrices may be computed for otherportions of the frequency band and transmitted to the base station usingsubsequent SRS transmissions, thereby allowing the base station toeventually receive the R_(nn) for more portions (e.g., all portions) ofthe SRS frequency. Accordingly, in such embodiments, differentpre-whitened SRSs are transmitted at different times using differentR_(nn) matrices to precode each SRS, each R_(nn) being computed andcorresponding to different portion(s) of the frequency band that is usedfor transmitting SRS.

Certain embodiments described herein relate to enabling the UE todetermine which portions of the SRS frequency band to use to compute theR_(nn) with each SRS transmission. In certain aspects, a UE may beconfigured (e.g., at the factory, pre-configured, configured over theair, by a message received from a base station, etc.) with and storeinformation indicative of one or more configurations of portions of oneor more frequency bands for use in computing R_(nn). For example, the UEmay be configured with a configuration that directs the UE to computeR_(nn) for odd RBs, a configuration that directs the UE to computeR_(nn) for even RBs, a configuration that directs the UE to computeR_(nn) for a particular frequency resource, etc.

A base station may be configured to signal which configuration to use tocompute R_(nn) and precode SRS using the computed R_(nn). In certainaspects, the base station signals such configuration selectioninformation or the configuration itself in a message (e.g., a commandthat triggers the SRS transmission (such as downlink control information(DCI) scheduling aperiodic SRS)). In certain aspects, the configurationselection information may include an indicator or identifier associatedwith the configuration. In certain aspects, the configuration mayindicate which portion(s) of the SRS frequency band to transmit at agiven time. For example, in some aspects, at different times, SRS may betransmitted in different portions of the frequency band allocated totransmit SRS. In some aspects, the portions of SRS frequency band,indicated in a configuration, nay be the same as the portions of the SRSfrequency band used to compute R_(nn).

In some aspects, a configuration may indicate the sequence of frequencyresources (e.g., RBs) over which R_(nn) is to be computed. For example,if the allocated SRS frequency bandwidth comprises 10 RBs, theconfiguration may indicate that the UE may compute the R_(nn) over a setof non-contiguous RBs of the SRS frequency bandwidth (e.g., every otherRBs of the 10 RBs of the SRS frequency bandwidth). As another example,the configuration may indicate that the UE may compute the R_(nn) over acontiguous number of RBs in the SRS frequency bandwidth (e.g., the firsthalf of the RBs in the 10 RBs of the SRS frequency bandwidth).

In some embodiments, the sequence of frequency resources (e.g., RBs)over which R_(nn) is computed may be a function of the number of thetimes SRS is to be transmitted (e.g., number of SRS symbols). Forexample, if the SRS is transmitted more times, then a finer sweep of thesystem bandwidth may be possible, such that for one SRS transmission theR_(nn) may be computed over some frequency resources and for the nextSRS symbol the R_(nn) may be computed over some other frequencyresources. In certain aspects, all frequency resources of the frequencyband allocated for transmitting SRS are used to compute R_(nn) over thecourse of all of the SRS symbols.

In some embodiments, the sequence and portions of the system bandwidthover which R_(nn) is computed may be a function of the SRS bandwidth,i.e., the bandwidth of the frequency band allocated for transmittingSRS. For example, if the SRS frequency bandwidth is a narrowband, thenR_(nn) may be computed over all the RBs of the SRS narrowband, in whichcase the R_(nn) bandwidth used for computing R_(nn) equals the SRSfrequency bandwidth. However, if the SRS frequency bandwidth is awideband, then R_(nn) may be computed over only a subset or subsamplingof the RBs within the SRS frequency wideband, in which case the Rimbandwidth is as large as only a fraction of the SRS frequency bandwidth.

In some embodiments, the sequence and portions of the SRS frequency bandover which R_(nn) is computed may be a function of timing (e.g., theamount of time the UE has to perform R_(nn) computations) and/or thecapabilities of the UE. For example, in some embodiments, the UE may betriggered to transmit SRS at a certain point in time either due to aperiodic SRS configuration or a signaling command including DCI forscheduling aperiodic SRS. At some point between when the UE is triggeredto transmit the SRS and when it is actually scheduled to transmit theSRS, the UE may receive signals, such as CSR, CSI-RS, ZP-CSI-RS, etc.,which the UE may use to estimate R_(nn).

Accordingly, the UE may perform its R_(nn) computations from the time itreceives these signals to when it transmits SRS. It is during this timeperiod when, in some embodiments, the UE determines which portion of theSRS frequency band to select to perform R_(nn) computations for thescheduled SRS. In some embodiments, during the same time period, the UEmay also determine a subsequent portion of the SRS frequency band toperform R_(nn) computations for the next scheduled SRS transmission(e.g., SRS that is transmitted in a subsequent subframe). In someembodiments, the determination about which subsequent portion of the SRSfrequency band to use for performing R_(nn) computations may beperformed after the first scheduled SRS transmission.

As described above, in embodiments where little time is available tocomplete the R_(nn) computations that are needed before transmitting theSRS, the UE may simplify the computations by estimating R_(nn) over asmaller bandwidth. As an example, in some embodiments, there may noteven be enough time for performing any R_(nn) computations, in whichcase the SRS that is transmitted may not be coded with R_(nn) and R_(nn)may be transmitted separately. However, when relatively more time isavailable for performing R_(nn) computations, the R_(nn) may be computedover a larger bandwidth. In addition, in some embodiments, the amount oftime that a UE needs to perform R_(nn) computations may depend on thecapabilities of the UE. If the UE is able to compute R_(nn) within avery short time span, then R_(nn) computations may be performed in caseswhere a less capable UE would not have performed such computations.

In some embodiments, the amount of time that the UE has to performR_(nn) computations (e.g., the amount of time starting from when the UEreceives signals (e.g., CRS etc.) to when it transmits SRS) may beconfigured or selected dynamically from among a set of configuredrelations as part of the same trigger that causes the SRS transmission.

In some embodiments, when the UE is triggered to transmit the SRS at acertain point in time and over a certain bandwidth, the UE may onlytransmit the SRS in frequency resources (e.g., RBs) for which R_(nn) hasbeen computed by the UE. For example, the SRS may be scheduled to betransmitted over a span of 10 RBs while R_(nn) may only be computed bythe UE for the first half of those RBs (e.g., the first 5 RBs of those10 RBs). In such an example, the SRS may also only be transmitted overthe first half of the RBs. Also, in such an example, during a subsequentSRS scheduled transmission, the SRS may be transmitted over the secondhalf of those 10 RBs, for which the UE is able to compute the R_(nn) aswell. Such a partitioning of the SRS bandwidth may depend on theconfiguration of the downlink reference signal (DL RS) used to estimatedownlink channel and interference (e.g., CSI-RS or ZP-CSI-RS), e.g., maydepend on or correspond to a similar bandwidth-based split in the CSI-RStransmission.

In some embodiments, different R_(nn) matrices may be used for precodingdifferent parts of the SRS bandwidth. For example, different frequencyresources (e.g., RBs) of the SRS frequency bandwidth may be coded with aR_(nn) computed for that frequency resource or a different frequencyresource. In certain aspects, this may negatively impact thelow-peak-to-average-power (low-PAPR) property of the SRS waveform.However, in certain aspects, UEs that are not near the cell-edge may beconfigured to use different R_(nn) matrices for coding different partsof the SRS frequency bandwidth as low peak-to-average power ration(low-PAPR) may not be as important, while in certain aspects, UEs nearthe cell edge may apply the same R_(nn) matrices for coding all parts ofthe SRS frequency bandwidth transmitted. It is important to note thatall the embodiments described above in relation to limiting the numberof RBs over which Rim is computed may be applied to embodiments wheredifferent matrices are used for precoding different parts of the SRSbandwidth.

Accordingly, using a multi-stage R_(nn) feedback, as described above inthe embodiments above, reduces the computation complexity involved incomputing the R_(nn) and, therefore, the amount of time and computerresources required to compute the R_(nn).

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: a, b, or c” is intended to cover a, b, c,a-b, a-c, b-c, and a-b-c, as well as any combination with multiples ofthe same element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b,b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c).

As used herein, the term “determining” encompasses a wide variety ofactions. For example, “determining” may include calculating, computing,processing, deriving, investigating, looking up (e.g., looking up in atable, a database or another data structure), ascertaining and the like.Also, “determining” may include receiving (e.g., receiving information),accessing (e.g., accessing data in a memory) and the like. Also,“determining” may include resolving, selecting, choosing, establishingand the like.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but is to be accorded the full scope consistentwith the language claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” Unless specifically statedotherwise, the term “some” refers to one or more. All structural andfunctional equivalents to the elements of the various aspects describedthroughout this disclosure that are known or later come to be known tothose of ordinary skill in the art are expressly incorporated herein byreference and are intended to be encompassed by the claims. Moreover,nothing disclosed herein is intended to be dedicated to the publicregardless of whether such disclosure is explicitly recited in theclaims. No claim element is to be construed under the provisions of 35U.S.C. § 112, sixth paragraph, unless the element is expressly recitedusing the phrase “means for” or, in the case of a method claim, theelement is recited using the phrase “step for.”

The various operations of methods described above may be performed byany suitable means capable of performing the corresponding functions.The means may include various hardware and/or software component(s)and/or module(s), including, but not limited to a circuit, anapplication specific integrated circuit (ASIC), or processor. Generally,where there are operations illustrated in figures, those operations mayhave corresponding counterpart means-plus-function components withsimilar numbering.

For example, means for transmitting and/or means for receiving maycomprise one or more of a transmit processor 420, a TX MIMO processor430, a receive processor 438, or antenna(s) 434 of the base station 110and/or the transmit processor 464, a TX MIMO processor 466, a receiveprocessor 458, or antenna(s) 452 of the user equipment 120.Additionally, means for generating, means for multiplexing, and/or meansfor applying may comprise one or more processors, such as thecontroller/processor 440 of the base station 110 and/or thecontroller/processor 480 of the user equipment 120.

The various illustrative logical blocks, modules and circuits describedin connection with the present disclosure may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array (FPGA) or other programmable logic device (PLD),discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general-purpose processor may be a microprocessor, but in thealternative, the processor may be any commercially available processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

If implemented in hardware, an example hardware configuration maycomprise a processing system in a wireless node. The processing systemmay be implemented with a bus architecture. The bus may include anynumber of interconnecting buses and bridges depending on the specificapplication of the processing system and the overall design constraints.The bus may link together various circuits including a processor,machine-readable media, and a bus interface. The bus interface may beused to connect a network adapter, among other things, to the processingsystem via the bus. The network adapter may be used to implement thesignal processing functions of the PHY layer. In the case of a userterminal 120 (see FIG. 1), a user interface (e.g., keypad, display,mouse, joystick, etc.) may also be connected to the bus. The bus mayalso link various other circuits such as timing sources, peripherals,voltage regulators, power management circuits, and the like, which arewell known in the art, and therefore, will not be described any further.The processor may be implemented with one or more general-purpose and/orspecial-purpose processors. Examples include microprocessors,microcontrollers, DSP processors, and other circuitry that can executesoftware. Those skilled in the art will recognize how best to implementthe described functionality for the processing system depending on theparticular application and the overall design constraints imposed on theoverall system.

If implemented in software, the functions may be stored or transmittedover as one or more instructions or code on a computer readable medium.Software shall be construed broadly to mean instructions, data, or anycombination thereof, whether referred to as software, firmware,middleware, microcode, hardware description language, or otherwise.Computer-readable media include both computer storage media andcommunication media including any medium that facilitates transfer of acomputer program from one place to another. The processor may beresponsible for managing the bus and general processing, including theexecution of software modules stored on the machine-readable storagemedia. A computer-readable storage medium may be coupled to a processorsuch that the processor can read information from, and write informationto, the storage medium. In the alternative, the storage medium may beintegral to the processor. By way of example, the machine-readable mediamay include a transmission line, a carrier wave modulated by data,and/or a computer readable storage medium with instructions storedthereon separate from the wireless node, all of which may be accessed bythe processor through the bus interface. Alternatively, or in addition,the machine-readable media, or any portion thereof, may be integratedinto the processor, such as the case may be with cache and/or generalregister files. Examples of machine-readable storage media may include,by way of example, RAM (Random Access Memory), flash memory, ROM (ReadOnly Memory), PROM (Programmable Read-Only Memory), EPROM (ErasableProgrammable Read-Only Memory), EEPROM (Electrically ErasableProgrammable Read-Only Memory), registers, magnetic disks, opticaldisks, hard drives, or any other suitable storage medium, or anycombination thereof. The machine-readable media may be embodied in acomputer-program product.

A software module may comprise a single instruction, or manyinstructions, and may be distributed over several different codesegments, among different programs, and across multiple storage media.The computer-readable media may comprise a number of software modules.The software modules include instructions that, when executed by anapparatus such as a processor, cause the processing system to performvarious functions. The software modules may include a transmissionmodule and a receiving module. Each software module may reside in asingle storage device or be distributed across multiple storage devices.By way of example, a software module may be loaded into RAM from a harddrive when a triggering event occurs. During execution of the softwaremodule, the processor may load some of the instructions into cache toincrease access speed. One or more cache lines may then be loaded into ageneral register file for execution by the processor. When referring tothe functionality of a software module below, it will be understood thatsuch functionality is implemented by the processor when executinginstructions from that software module.

Also, any connection is properly termed a computer-readable medium. Forexample, if the software is transmitted from a website, server, or otherremote source using a coaxial cable, fiber optic cable, twisted pair,digital subscriber line (DSL), or wireless technologies such as infrared(IR), radio, and microwave, then the coaxial cable, fiber optic cable,twisted pair, DSL, or wireless technologies such as infrared, radio, andmicrowave are included in the definition of medium. Disk and disc, asused herein, include compact disc (CD), laser disc, optical disc,digital versatile disc (DVD), floppy disk, and Blu-ray® disc where disksusually reproduce data magnetically, while discs reproduce dataoptically with lasers. Thus, in some aspects computer-readable media maycomprise non-transitory computer-readable media (e.g., tangible media).In addition, for other aspects computer-readable media may comprisetransitory computer-readable media (e.g., a signal). Combinations of theabove should also be included within the scope of computer-readablemedia.

Thus, certain aspects may comprise a computer program product forperforming the operations presented herein. For example, such a computerprogram product may comprise a computer-readable medium havinginstructions stored (and/or encoded) thereon, the instructions beingexecutable by one or more processors to perform the operations describedherein.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein can bedownloaded and/or otherwise obtained by a user terminal and/or basestation as applicable. For example, such a device can be coupled to aserver to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via storage means (e.g., RAM, ROM, a physical storage mediumsuch as a compact disc (CD) or floppy disk, etc.), such that a userterminal and/or base station can obtain the various methods uponcoupling or providing the storage means to the device. Moreover, anyother suitable technique for providing the methods and techniquesdescribed herein to a device can be utilized.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes and variations may be made in the arrangement, operation anddetails of the methods and apparatus described above without departingfrom the scope of the claims.

What is claimed is:
 1. A method of wireless communications for use by auser equipment (UE), comprising: receiving, from a base station, one ormore signals for use in estimating channel quality for a downlinkbetween the base station and the UE; and transmitting a first referencesignal (RS) precoded with a first downlink channel quality estimate,wherein: the first RS comprises the first downlink channel qualityestimate, the first downlink channel quality estimate is based on afirst frequency resource of the one or more signals, and a frequencyband allocated for RS transmission includes the first frequencyresource.
 2. The method of claim 1, further comprising: transmitting asecond reference signal (RS) precoded with a second downlink channelquality estimate, wherein: the second RS comprises the second downlinkchannel quality estimate, the second downlink channel quality estimateis based on a second frequency resource of the one or more signals, andthe frequency band allocated for RS transmission includes the secondfrequency resource.
 3. The method of claim 2, wherein the first downlinkchannel quality estimate comprises a first interference covariancematrix (R_(nn)) and the second downlink channel quality estimatecomprises a second R_(nn), and wherein the first RS comprises a firstsounding reference signal (SRS) and the second RS comprises a secondSRS.
 4. The method of claim 2, wherein the first frequency resource andthe second frequency resource are determined based on a message receivedfrom the base station for triggering the UE to perform a RStransmission.
 5. The method of claim 4, wherein the message comprisesdownlink control information for sounding reference signal (SRS)scheduling.
 6. The method of claim 4, wherein the message identifies oneof a plurality of configurations, each configuration corresponding to adifferent set of frequency resources.
 7. The method of claim 2, whereinthe first frequency resource and the second frequency resource aredetermined based on a range of the frequency band allocated for RStransmission.
 8. The method of claim 2, wherein the first frequencyresource and the second frequency resource are determined based oncapabilities of the UE.
 9. The method of claim 2, wherein the firstfrequency resource and the second frequency resource are determinedbased on time available between events of receiving a message indicatingtransmission of RS, receiving the one or more signals for use inestimating the channel quality, and transmitting the first RS.
 10. Themethod of claim 1, wherein the frequency band allocated for RStransmission comprises resource blocks (RBs).
 11. The method of claim 1,wherein: transmitting the first RS comprises transmitting the first RSover all frequency resources of the frequency band; and the firstfrequency resource corresponds to all frequency resources of thefrequency band.
 12. The method of claim 1, wherein: transmitting thefirst RS comprises transmitting the first RS over all frequencyresources of the frequency band at a first time; and the first frequencyresource corresponds to a first subset of the frequency resources of thefrequency band.
 13. The method of claim 12, further comprising:transmitting a second RS precoded with a second downlink channel qualityestimate, wherein: the second RS comprises the second downlink channelquality estimate, the second downlink channel quality estimate is basedon a second frequency resource of the one or more signals, the frequencyband allocated for RS transmission includes the second frequencyresource, transmitting the second RS comprises transmitting the secondRS over all the frequency resources of the frequency band at a secondtime, and the second frequency resource corresponds to a second subsetof the frequency resources of the frequency band.
 14. The method ofclaim 1, wherein: transmitting the first RS comprises transmitting thefirst RS over the first frequency resource; and the first frequencyresource corresponds to a first subset of the frequency resources of thefrequency band.
 15. The method of claim 14, further comprising:transmitting a second RS precoded with a second downlink channel qualityestimate, wherein: the second RS comprises the second downlink channelquality estimate, the second downlink channel quality estimate is basedon a second frequency resource of the one or more signals, the frequencyband allocated for RS transmission includes the second frequencyresource, transmitting the second RS comprises transmitting the secondRS the second frequency resource, and the second frequency resourcecorresponds to a second subset of the frequency resources of thefrequency band.
 16. A user equipment (UE), comprising: a memory; and aprocessor coupled to the memory, the processor and the memory areconfigured to: receive, from a base station, one or more signals for usein estimating channel quality for a downlink between the base stationand the UE; and transmit a first reference signal (RS) precoded with afirst downlink channel quality estimate, wherein: the first RS comprisesthe first downlink channel quality estimate, the first downlink channelquality estimate is based on a first frequency resource of the one ormore signals, and a frequency band allocated for RS transmissionincludes the first frequency resource.
 17. The UE of claim 16, whereinthe memory and the processor are further configured to: transmit asecond reference signal (RS) precoded with a second downlink channelquality estimate, wherein: the second RS comprises the second downlinkchannel quality estimate, the second downlink channel quality estimateis based on a second frequency resource of the one or more signals, andthe frequency band allocated for RS transmission includes the secondfrequency resource.
 18. The UE of claim 17, wherein the first downlinkchannel quality estimate comprises a first interference covariancematrix (R_(nn)) and the second downlink channel quality estimatecomprises a second R_(nn), and wherein the first RS comprises a firstsounding reference signal (SRS) and the second RS comprises a secondSRS.
 19. The UE of claim 17, wherein the first frequency resource andthe second frequency resource are determined based on a message receivedfrom the base station for triggering the UE to perform a RStransmission.
 20. The UE of claim 19, wherein the message comprisesdownlink control information for sounding reference signal (SRS)scheduling.
 21. The UE of claim 19, wherein the message identifies oneof a plurality of configurations, each configuration corresponding to adifferent set of frequency resources.
 22. The UE of claim 17, whereinthe first frequency resource and the second frequency resource aredetermined based on a range of the frequency band allocated for RStransmission.
 23. The UE of claim 17, wherein the first frequencyresource and the second frequency resource are determined based oncapabilities of the UE.
 24. The UE of claim 17, wherein the firstfrequency resource and the second frequency resource are determinedbased on time available between events of receiving a message indicatingtransmission of RS, receiving the one or more signals for use inestimating the channel quality, and transmitting the first RS.
 25. TheUE of claim 16, wherein the frequency band allocated for RS transmissioncomprises resource blocks (RBs).
 26. The UE of claim 16, wherein: theprocessor and the memory being configured to transmit the first RScomprises the processor and the memory being configured to transmit thefirst RS over all frequency resources of the frequency band; and thefirst frequency resource corresponds to all frequency resources of thefrequency band.
 27. The UE of claim 16, wherein: the processor and thememory being configured to transmit the first RS comprises the processorand the memory being configured to transmit the first RS over allfrequency resources of the frequency band at a first time; and the firstfrequency resource corresponds to a first subset of the frequencyresources of the frequency band.
 28. The UE of claim 27, wherein theprocessor and the memory are further configured: transmit a second RSprecoded with a second downlink channel quality estimate, wherein: thesecond RS comprises the second downlink channel quality estimate, thesecond downlink channel quality estimate is based on a second frequencyresource of the one or more signals, the frequency band allocated for RStransmission includes the second frequency resource, the processor andthe memory being configured to transmit the second RS comprises theprocessor and the memory being configured to transmit the second RS overall the frequency resources of the frequency band at a second time, andthe second frequency resource corresponds to a second subset of thefrequency resources of the frequency band.
 29. The UE of claim 16,wherein: the processor and the memory being configured to transmit thefirst RS comprises the processor and the memory being configured totransmit the first RS over the first frequency resource; and the firstfrequency resource corresponds to a first subset of the frequencyresources of the frequency band.
 30. The UE of claim 29, wherein theprocessor and the memory are further configured to: transmit a second RSprecoded with a second downlink channel quality estimate, wherein: thesecond RS comprises the second downlink channel quality estimate, thesecond downlink channel quality estimate is based on a second frequencyresource of the one or more signals, the frequency band allocated for RStransmission includes the second frequency resource, the processor andthe memory being configured to transmit the second RS comprises theprocessor and the memory being configured to transmit the second RS thesecond frequency resource, and the second frequency resource correspondsto a second subset of the frequency resources of the frequency band.